Adjustable inductance and coupling system



June 16, 1931. L. A. GEBHARD 1,809,932

ADJUSTABLE INDUCTANCE AND COUPLING SYSTEM Filed June 5, 1929 2 Sheets-Sheet 1 TE L 5 com:

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A TTORNEY June 16, 1931. L. A. GEBHARD 1,809,932

ADJUSTABLE INDUCTANCE AND COUPLING SYSTEM Filed June 5, 1929 2 Sheets-Sheet 2 INVENTOR. 04444 0L, gwfifzovu),

BY Eula ATTORNEY at... June is, 1931 UNITED STATES PATENT orrlcr.

LOUIS A. GEBHARD, OF WASHINGTON, DISTRICT OF COLUMBIA, ASBIGNOR '.I.'O wmnn RADIO, INC 01 NEW YORK, N. Y., A CORPORATION OF DELAWARE ADJUSTABLE INDUCTAN C11 AND OOUPLHQ'G BYB'I'EE Application filed June 5, 1929, Serial No. 808,880.

My invention relates broadly to adjustable inductance and more particularly to coupling systems for high frequency radio transmitters.

One of the objects of my invention is to providea combination adjustable inductance and coupling system.

Another object of my invention is to provide a compact and efiicient adjustable inductance and coupling system wherein the coupling is automatically controlled by effecting diflerent adjustments of inductance.

Other and further objects of my invention are to provide certain structural features for, an adjustable inductance and coupling system whereby changes in the inductance and coupling may be easily and readily effected.

My invention will be more fully understood from the specification hereinafter following by reference to the accompanying drawings wherein:

Figure 1 shows a side elevation partly in central vertical longitudinal section of the inductance and coupling system of my invention; Fig. 2 shows a horizontal view of the inductance system of my invention on line 2-2 of Fig. 1 with parts broken away and in, section; and Fig. 3 shows a portion of the. inductance and coupling system of my invention in greater detail as a section on line 33 of Fig. 1.

A given coil system employed in high frequency radio transmitters will usually cover but a limited frequency band. In order to cover such a wide band, as for instance 1,000 to 20,000 kilocycles, it is necessary to have a plurality of coils having different freguency characteristics, which may be selectively introduced into the circuit for operating on different successive frequencies in the frequency band. The inductance coils must be of such design as to afford the proper frequency characteristics as well as being of the correct design to provide proper coupling characteristics to external circuits. Difiiculty is encountered in obtaining the proper flexibility of frequency characteristics where the coupling is desired from the output circuit of a simple thermionic tube amplifier to the input circuit of a balanced thermionic tube amplifier circuit. Other circuit arr ment sometimes present certain difliculties in coupling which may be advantageously overcome by the adjustable inductance and coupling system of m invention. Figs. 1 and 2 o the accompanying drawlngs show a side elevation and an end view respectively 'of a four coil inductance system. Any number of coils may be employed depending upon the particular application of my invention. The respective main induc tance coils 1, 2, 3 and 4 are suspended from and are parallel to a shaft 5. Coils 1, 2, 3 and 4 are mounted equidistant from the center line of the shaft 5 and so arran d that their respective members 6, 7 ,8 an 9 will engage with stationary contacts 10 when the shaft isrotated by means of handle 11.

Shaft 5 is suspended in bearings 12 and 13 which are mounted on the framework of the radio transmitter. It will often be convenient to mount the inductance unit on the panel of a radio transmitter so that bearing 13 will be the front panel of the radio transmitter having an indicating system such as dial 14 to indicate the particular coil in the circuit.

Figure 1 of the drawin shows certain structural features in detai Each coil unit comprises annular members 15 and 16 on which'are mounted coil s acers 17 Spacers 17 are of suitable insulating material. The main inductances proper comprise individual lengths of metal wound in helical formation over spacers 17 and may be of the flat wound type as shown at 18a or of the edgewise wound type as shown at 186. C0 per tubing or round rod may be employed if desired. Each of coils 1, 2, 3- and 4 is associated with an individual coupling coil. The coupling coils are of lesser diameters than are the main inductance coils. Coils 19a and 190 are two of such coils which are supported inside of inductances 18a and 180, respectively. The coupling coils are made of heavy enough material to be self-supporting and are electrically insulated from the main inductance coils. Coils 19a and 190 are normally employed as coupling coils in the sense that they are usually connected for coupling to the preceding stage and provide for the transfer of energy between the output of one am lifier circuit to the input of another. nductance coils 18a, 18b, 180 and 18d may be the inductances employed in the output circuits of thermionic tube amplifiers, or may be the input circuits for succeeding amplifiers. Such inductance coils are adjusted to have certain frequency characteristics in cooperation with the circuit by means of a variable condenser.

The coupling coils 19a, 19b, 19c and 19d are arranged so that they are centralized both longitudinally and crosswise, with respect to coils 18a, 18b, 18c and 18d. This is necessary to prevent any unbalancing in the coupling to either half of the input circuit in a balanced thermionic tube circuit. Coils 19a, 19b, 19c and 19d are arranged to have an air space, as shown at 25 to reduce the electrostatic coupling to the coils 18a, 18b, 18c and 18d, respectively. Coils 19a, 19b, 19c and 19d can have diameters as small as practicable, while coils 18a, 18b, 18c, and 1811 have as large diameters as possible consistent with the limitations imposed by the range of frequency desired and space available. A center tap is provided on coils 18a, 186, 180 and 18d as shown on coil 18a at 90'. Center tap contact member 90 is shown engaged with contact 100. Stationarycontactmember10cis mounted together with contacts 10a, 10b, 10d and 10 on insulating member 20. Contacts 10a, 10b, 10c, 10d and 10 are connected to the external circuits involved. The contacts 9a and 9 form the terminals for coil 19a and are arranged to afford minimum capacity with relation to the terminals. 9?) and 9d of coil 18a and contacts 8a and 8, 7a and 7, are similarly arranged. Any appreciable capacity at this point tends to unbalance the balanced system. Coils 19?), 19c and 19d are connected with contacts similar to contacts 9a and 9.

' Coils, 1, 2, 3 and 4 may be arranged so as to be easily removable for adjustment or repair. In the arrangement shown coil 4 can be removed by removing screws 21. End plates 22 are of suitable insulating material and may be removed from parts 15 and 16 by removing screws 23 and nuts 23a, the latter holding coils 19a in place. This permits the removal of coils 19a, 19b, 19c and 19d. The hub 24 together with shaft 5 is made of suitable insulating material to reduce distributed capacities to a minimum. Hub 24 is fastened to shaft 5 by means of collars 26.

Fig. 2 shows certain structural features in greater detail. The end supporting member for coil 1 and hub 24 is here shown removed. The space between coupling coil 19d and insulating spacers 17 is clearly shown. Contact members 9, 8, 7 and 6 are connected with coils 19a, 1961,190 and 196, respectively.

.Fig. 3 shows a section of the inductance system of my invention representing a combination switching mechanism and means for exerting a retaining force against the movement of the coils. Contact members 27 are controlled by spring member 28. Spring member 28 comprises a strip of suitable spring metal provided with an indented portion 29. Portion 29 of spring 28 bears against the periphery of disk 30. Disk 30 is provided with notches 31 arranged around the periphery, the number of such notches corresponding to the number of coils employed. Disk 30 is attached to shaft 5 and is movable with respect to panel or framework 13. Contacts 27 may be electrically related with the starter circuit of the high frequency transmitter or the sources of energizing potential for the transmitter. Contacts 27 are actuated slightly before the disengagement of the contacts carried b the movable coils, in this manner preventing sparking and the resulting injury to the coil contacts and associated stationary contacts.

The adjustable inductance system of my invention has many advantages over other inductance systems. The coupling coils 19a, 196, 190 and 19d have different frequency characteristics which depend upon the circuit to be electrically related therewith, the frequency of the energy in coils 1, 2, 3 and 4 and other factors which should be taken into consideration in the initial design. It is often desirable to couple the ener y from one circuit to another when one or both circuits are symmetrical or both circuits unsymmetrical. This necessitates a coupling system adapted to great flexibility of operation. The degree and type of coupling may be varied with different frequencies of operation and by this means efliciency maintained over a relatively wide band of frequencies.

While I have described my invention in one of its preferred embodiments, I desire that it be understood that modifications may be made and that no limitations upon my invention are intended other than are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. An adjustable inductance system comprising in combination a rotatable framework carrying a plurality of helical main inductance coils wound with spaced turns and adapted to carry currents of the magnitude used in radio transmitting sets, each of said coils having frame contact members therefor mounted on said rotatable frame, stationary contact members adapted to engage said frame contact members, and a plurality of auxiliary inductance coils each in individual electromagnetic relation with one of said main inductance coils.

2. An adjustable inductance system comprising in combination a plurality of helical main inductance coils wound with spaced turns positioned on a movable framework, frame contact members for each of said coils, stationary contact members adapted to engage said frame contact members, and a plurality of auxiliary inductance coils respectively in inductive relation with said main inductance coils.

3. An adjustable inductance system comprising in combination a plurality of helical main inductance coils carried by a movable framework, said coils being wound with spaced turns and adapted to carry currents of the magnitude used in radio transmitting sets, each of said coils having different inductance values, and a plurality of auxiliary inductance coils respectively mounted coaxially with said main inductance coils.

4. An adjustable inductance system comprising in combination a plurality of helical main inductance coils carried by a'rotatable framework and adapted to be selectively connected with an external circuit and a plurality of auxiliary inductance coils each mounted within one of said main inductance coils and substantially coaxially therewith.

5. In a variable inductance system for radio frequency generators, a plurality of inductance units, a rotatable frame carrying said inductance units, each of said inductance units consistin of a pair of helical inductance elements aving spaced turns, one surrounding the other, the outer of said inductance elements being substantially larger than the inner, frame contact elements connected to each of said coils and fixed contact elements adapted to selectively engage each of said frame contact elements as said frame is'rotated, said contact elements for said inner inductance element being dielectrically remote from said contact elements for said outer inductance element, whereby electrostatic coupling between said inner and outer inductance elements is minimized.

LOUIS A. GEBHARD. 

